V. V. Klechkovskaya

Poly(acrylamide) gels with embedded magnetite nanoparticles

Magnetic gels are a new class of soft polymer materials with their properties controlled by magnetic fields. A method was developed for the preparation of magnetite nanoparticles in a matrix of poly(acrylamide) gel. Synthesis of the magnetic spinel iron oxide Fe3O4 in a matrix of poly(acrylamide) gel was performed via coprecipitation of Fe(II) and Fe(III) in alkaline medium. The effects of the cross-link density, the concentration of polymer and salt in the swollen network during preparation on the composition, structure and properties of the magnetic gels were studied by electronography, TEM and small-angle X-ray scattering (SAXS). The crystalline lattice of the particles was determined as magnetite. The average size of the particles, d, calculated from the half-width of the diffraction peaks, is of the order of 10 nm. The obtained data demonstrate a marked difference in size distribution of magnetic particles in gels of different structure.

Formation of magnetite nanoparticles in poly(acrylamide) gels

Magnetic gels with magnetite nanoparticles incorporated in a matrix of poly(acrylamide) gel were studied. Magnetite was synthesized through coprecipitation of Fe(II) and Fe(III) in the gel phase, in the solution of linear polymer and in aqueous solution without polymer in alkaline media. The effects of network structure and of the concentration of iron salts in the swollen networks on the composition, structure and properties of magnetic gels have been studied by electron diffraction, XRD, transmission electron microscopy and vibration sample magnetometry. The average size of magnetite nanoparticles, D, is of the order of 10 nm. It decreases with the increase of polymer concentration in the gel phase. In the dried gels the particles form spherical aggregates (diameter about 150 nm), whereas in the solution of linear polymer, in the aqueous solution of iron salts and in the gel with high content of polymer the aggregates have irregular shape.

Electron Diffraction Structure Analysis

Electron diffraction Structure Analysis is generally used to study thin films and finely dispersed crystalline materials and allows the complete structure determinations up to the establishment of the atomic coordinates in the crystal lattice and refinement of atomic thermal vibrations. At present various unknown crystal structures have been determined by the method of electron diffraction structure analysis. In this lecture the first stage of structure analysis - obtaining of appropriate diffraction patterns and their geometrical analysis is exmined.

Structure of cellulose Acetobacter xylinum

The data are presented on optimization of cellulose synthesis by Acetobacter xylinum (strain VKM V-880) and the structural characteristics of A. xylinum cellulose gel film synthesized during static cultivation. The structural changes caused by the removal of water from gel films are established and the structural organization of macromolecular chains in cellulose A. xylinum is studied.

Determination of the size and phase composition of silver nanoparticles in a gel film of bacterial cellulose by small-angle X-ray scattering, electron diffraction, and electron microscopy

The nanoscale structural features in a composite (gel film of Acetobacter Xylinum cellulose with adsorbed silver nanoparticles, stabilized by N-polyvinylpyrrolidone) have been investigated by small-angle X-ray scattering. The size distributions of inhomogeneities in the porous structure of the cellulose matrix and the size distributions of silver nanoparticles in the composite have been determined. It is shown that the sizes of synthesized nanoparticles correlate with the sizes of inhomogeneities in the gel film. Particles of larger size (with radii up to 100 nm) have also been found. Electron microscopy of thin cross sections of a dried composite layer showed that large particles are located on the cellulose layer surface. Electron diffraction revealed a crystal structure of silver nanoparticles in the composite.

Study of polyelectrolyte complexes of chitosan and sulfoethyl cellulose

The complexing of polycation chitosan and polyanion sulphoethyl cellulose during the formation of polyelectrolyte simplex membranes using the layer-by-layer deposition of a solution of one polyion on a gel-like film of another one has been studied. The structural characteristics of the multilayer composites and their components have been analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray microanalysis. A technique is proposed for studying the structure of surface layers of thin polymer films (15–20 μm) using a portable DIFREI-401 diffractometer. It is shown that the sequence of layer deposition during the formation of membrane films does not affect their structural characteristics. The interaction between positively charged chitosan groups (-NH3+) and negatively charged sulfoethyl cellulose groups (-SO3−) during the growth of polyelectrolyte complexes results in a packing of chitosan chains in the multilayer film.

Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.

Peculiarities of the microstructure of a nanoscale modification of η-TiO2

Samples with nanoscale η-TiO2 phase have been obtained by sulfate and modified sulfate methods and are characterized by a complex of techniques: X-ray diffraction, electron diffraction, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and X-ray energy-dispersive analysis. The effect of sample formation conditions on the size and shape of crystallites, content of the amorphous component in the samples, and their elemental composition has been established. A significant change (depending on the synthesis conditions) in the parameters of the diffraction reflection with d ∼ 17–21 Å (intensity and interplanar spacing d, Å), pronounced for η-TiO2, is revealed. This change is most likely related to the variation in the content of water molecules in the interlayer space of η-TiO2 structure and/or the change in crystallite shape.

Precipitates of MnSi cubic phase in tetragonal Mn4Si7 crystal

Higher manganese silicides (HMSs) exhibit interesting thermoelectric and optoelectronic properties. Development of HMS-based thermoelements and microthermopiles of different designs may meet a number of problems, which can be solved only when the real structure of crystals and thin layers on which they are based is established. We have applied scanning and transmission electron microscopy and electron diffraction to investigate HMS crystals of two types: single crystals grown from melt by the Bridgman method and microislands formed by reactive diffusion during manganese vapor deposition on silicon substrates. The exact phase composition of these materials is established: matrix HMS crystal belonging to tetragonal system (Mn4Si7 composition) and precipitates of cubic manganese monosilicide MnSi. The shape and sizes of precipitates are determined, the crystallographic relationships between the tetragonal and cubic phases are found, and the interface is investigated.

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films was studied. The optimal sorption parameters at which the amorphous form of the selenium complex is preserved in the composite were suggested.